swarmctl: on a controller host, trust the swarm's root without SWARMCTL_CA_FILE

`swarmctl login` (and any `--swarm` verb) on a controller host failed TLS
with `UnknownIssuer` against the swarm's own gateway: its leaf chains to
the store's `pki` root, which no system store holds, and the only way
through was `--ca-file`/`SWARMCTL_CA_FILE` by hand.

The host's swarmctl wrapper now sets `SSL_CERT_FILE` to the bundle the
swarm-controller daemon already trusts (`/run/swarm-controller-ca/
trust-bundle.pem`: system CAs plus the swarm's root), when the gateway is
self-signed. swarmctl's reqwest/rustls resolves roots the same way the
daemon's does, so this is the path the daemon uses to reach the same
gateway. `--set` rather than a default, since a nix shell exports its own
`SSL_CERT_FILE`.

Pointing `SWARMCTL_CA_FILE` at the bundle instead would not work (#5243):
`--ca-file` adds each certificate as a root and fails the whole client on
one it can't parse.

Hosts without the controller (an operator laptop) still need `--ca-file`.

Refs #5239
Fixes #5243

nix/host-modules/swarm-controller.nix

@@ -159,6 +159,15 @@ let
     gatewayCfg = config.services.hyperhive.gateway;
   };
 
+  # `swarmctl --swarm` (and `login`) reach the same gateway as the daemon,
+  # through the same `reqwest`/`rustls` roots, so the wrapper hands it the
+  # daemon's bundle. `--set`, not a default: a nix shell exports its own
+  # `SSL_CERT_FILE`, which would win and lack the swarm's root. The bundle
+  # holds the system CAs too, so public hosts still verify.
+  swarmctlTrustEnv = lib.optionalAttrs caTrust.useSelfSigned {
+    SSL_CERT_FILE = caTrust.bundlePathFor "swarm-controller";
+  };
+
   # The controller's own OAuth2 client. It is NOT a hive: the per-hive
   # clients the roster issues belong to hives, and the responder's client
   # belongs to the responder. One identity per principal — the rule is that
@@ -257,7 +266,7 @@ let
       wrapProgram $out/bin/swarmctl ${
         lib.concatStringsSep " " (
           lib.mapAttrsToList (name: value: "--set ${name} ${lib.escapeShellArg value}") (
-            controllerSocketEnv // deployCfg.swarm-controller.swarmctlEnvironment
+            controllerSocketEnv // swarmctlTrustEnv // deployCfg.swarm-controller.swarmctlEnvironment
           )
           ++ lib.mapAttrsToList (
             name: value: "--set-default ${name} ${lib.escapeShellArg value}"

nix/module-eval/bao-controller.nix

@@ -146,6 +146,12 @@ let
         && lib.hasInfix "--set-default SWARMCTL_LOGIN_DEFAULT_SWARM https://t.local" swarmctlWrapperCmd
         && !(lib.hasInfix "SWARMCTL_SWARM" swarmctlWrapperCmd);
     }
+    {
+      # The gateway's leaf chains to the store's root, which no system store
+      # holds; without the bundle `login` fails `UnknownIssuer`.
+      name = "the host's swarmctl trusts the swarm's root through the daemon's bundle";
+      ok = lib.hasInfix "--set SSL_CERT_FILE /run/swarm-controller-ca/trust-bundle.pem" swarmctlWrapperCmd;
+    }
     {
       name = "a swarm with no matrix gateway vhost gives the controller no homeserver variable";
       ok =

swarmctl/README.md

@@ -189,5 +189,8 @@ refuses it. When it can't be refreshed, any verb says to run `swarmctl login`
 again. To log out, delete the file.
 
 A swarm whose gateway serves a certificate from the swarm's own CA needs
-that CA: `--ca-file` or `SWARMCTL_CA_FILE`. The `user` verbs edit the local
+that CA. On a controller host the swarm-controller module's wrapper sets
+`SSL_CERT_FILE` to the bundle the daemon itself trusts (the system CAs plus
+the swarm's root), so nothing needs setting there. Elsewhere, pass the CA
+with `--ca-file` or `SWARMCTL_CA_FILE`. The `user` verbs edit the local
 users file and have no remote form.